This invention relates to methods and apparatus for completing a well. More specifically the present invention relates to methods and apparatus for reducing the amount of abrasive or blocking solid particles such as sand from subterranean formation entering the wellbore in either an initial completion of the well or in remedial operations to improve an initial completion.
Certain underground formations encountered in the drilling of wells such as oil and gas wells are sometimes prone to sanding during the production phase. Sand when produced along with the fluids from the formation can cause severe problems with the ability of the well to produce the desired fluids due to blockage by the produced solids and damage done to installations due to the abrasive nature of such particles.
Wellbores drilled in sanding-prone reservoirs can be completed either in a cased hole configuration or in an uncased (open-hole) configuration. For cased hole completions, a casing string, typically formed from a series of steel tubes joined end to end, is cemented in place in the wellbore. The simplest cement placement is primary cementing where a fluid train comprising a cement slurry is pumped from the surface into the wellbore through the casing string, returning towards the surface along the annular gap between the casing and the formation. The cement sets in the annulus behind the casing to form a material that supports and protects the casing and provides zonal isolation.
At present, open hole (uncased) reservoir completion of a sanding-prone reservoir is often a complicated and expensive procedure requiring the use of hardware to prevent the sand production from the reservoir during the production phase.
Common current ways to prevent sanding include;
gravel packing after placing tools and screens in the hole;
placement of a prepacked screen in the open hole;
use of expandable screen completions; and
reservoir sandface consolidation, for example using resin.
The gravel packing process requires the use of a special tool and incomplete placement of gravel is a well-known risk particularly in horizontal reservoirs. Pre-packed screens eliminate the risk of voids but require special complex placement.
U.S. Pat. No. 3,026,936 proposes to facilitate well production through the use of fractures in cement. Fracturing of cement in a vertical well is proposed by use of bullets, mechanical hammers, hydraulically activated pistons and casing deformation through increased hydraulic pressure. Additionally, increasing permeability is proposed by chemical treatment.
The use of casing liner with pre-weakened (plugged holes) zones is proposed in U.S. Pat. No. 4,531,583 which describes a cement placement method for remediation of channels between casing and cement. Another use of casing liner with pre-cut holes is described in the United States published patent application No. 2005/0121203 A1 as expanded liner to be brought into direct contact with the wellbore wall.